QUANTIM Streszczenie raportu

Precise assignment of classical and quantum features in "two-photon imaging"

The idea of entangled two-photon imaging (ghost imaging") was conceived some time ago by Klishko and inspired a number of beautiful experiments in the mid nineties. As is well known, spontaneous parametric down-conversion consists of an emission of correlated pairs of signal and idler photons. One inserts in the signal arm an object that one intends to observe. The image of this object is obtained in a rather paradoxical way, without using a pixellised detector, but instead a single, non imaging, detector on the signal beam.

On the other hand, one inserts a pixellised detector (i.e. a camera) in the idler arm where there is no object. The entangled imaging technique realizes the observation of the object by detecting the coincidences between the measured photons on the signal and idler beams. The BU group gave, at the beginning of this project, a comprehensive theory of this phenomenon which allowed INFM and BU to make further progress in its understanding. It was for example shown by INFM that one could also produce the same imaging in the continuous variable regime, i.e. by using the correlation between photocurrents, and that both the near field and the far field images could be imaged in the same experimental set-up. Following R. Boyd's experiment which was able to obtain a near field image using classically correlated beams, and not twin photons, a lively worldwide discussion started on the precise assignment of classical and quantum features in "two-photon imaging".

These investigations led INFM to a very surprising and spectacular result: the discovery that the same imaging technique could be made, both in the near field and in the far field, by using classical correlated beams, such as a thermal beam divided in two parts on a beam splitter, instead of quantum correlated beams.

In the spring of 2004, the INFM group succeeded in making an experiment demonstrating the reconstruction of the image, both in the near and far field, in a ghost imaging scheme based on the classical correlation between two thermal-like light beams.